Browsing by Author "STANLEY, DW"

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    HARD-TO-COOK DEFECT IN BLACK BEANS - PEROXIDASE CHARACTERIZATION AND EFFECT OF HEAT PRETREATMENT AND STORAGE-CONDITIONS ON ENZYME INACTIVATION
    (1989) RIVERA, JA; HOHLBERG, AI; AGUILERA, JM; PLHAK, LC; STANLEY, DW
    Black beans (Phaseolus vulgaris) were studied in order to characterize the soluble peroxidase (POD) activity and to determine the effect of heat pretreatment and storage conditions on hardening and enzyme inactivation. Bean POD activity demonstrated a pH optimum from 6.4 to 6.8, an optimum temperature between 40 and 45.degree.C, an activation energy of 1.19 kJ/mol, a strong dependence on water activity and little sensitivity to added calcium ions. Beans stored at 30.degree.C/85%RH exhibited a 30-50% reduction in POD activity compared to samples kept at 15.degree.C/35%RH but this may not reflect in vivo rates. Thermal inactivation of POD activity in bean flour was facilitated at increasing moisture levels. A heat pretreatment of beans at moisture contents not exceeding 13% failed to control hardening in beans subsequently stored at temperatures of 27.degree.C or above and moisture levels of 13%. While no POD activity was found at heat pretreatment equilibrium temperatures above 102.degree.C and none of the samples that had acceptable hardening values demonstrated POD activity, increasing equilibrium temperature above 105.degree.C continued to reduce hardness. Thus, heating to only inactivate POD was not sufficient and higher temperatures were required to inactivate the hardening mechanism.
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    HARD-TO-COOK DEFECT IN BLACK BEANS - PROTEIN AND STARCH CONSIDERATIONS
    (1987) HOHLBERG, AI; STANLEY, DW
    Black beans (Phaseolus vulgaris) was stored for 10 months under three environmental conditions [high temperature/humidity (HTHH: 30.degree.C, 85% RH); medium temperature/humidity (MTMH: 25.degree.C, 65% RH); low temperature/humidity (LTLH: 15.degree.C, 35% RH)] in order to determine changes in starch and protein and to assess their contribution in textural defects. Hard-to-cook defect developed in HTHH-stored seeds and partially in MTMH samples. An increase in the DSC peak starch gelatinization temperature during storage at all three conditions was not related to hardening. Five protein fractions were separated by gel filtration. A significant increase (p < 0.05) was found during storage for a low-MW fraction of HTHH and MTMH extracts. At the same time a high-MW fraction decreased significantly (p < 0.05), suggesting the breakdown of large proteins. After 10 months of storage, free aromatic amino acids increased significantly (p < 0.05) with increasing temperature and humidity of storage. The coincidence of the appearance of small polypeptides and aromatic amino acids with the development of the hard-to-cook defect suggested a relation between these phenomena.
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    MODELING OF BEAN HARDENING KINETICS DURING STORAGE
    (FOOD NUTRITION PRESS INC, 1993) DELVALLE, JM; AGUILERA, JM; HOHLBERG, AI; RICHARDSON, JC; STANLEY, DW
    Two kinetic models ('empirical' and 'logistic') were adapted to predict storage-induced hardening of black and white beans, A database consisting of 451 observations gathered using black bean samples at 38 different storage conditions and 155 experimental data points corresponding to white beans stored at 12 different conditions was utilized to validate the proposed equations. Compared to other published models, the ones developed in this study were not limited to mild storage conditions or short storage times. Hardening showed an initial lag period, followed by a period of fast hardening, and ending in a period of declining hardening rate as hardness plateaued to equilibrium values at adverse storage conditions. Hardening rates increased with either the water activity of beans or storage temperature, whereas equilibrium values were only determined by sample water activity, for black beans, or temperature, for white beans. Both models used the activation energy and equilibrium constant of the hardening reaction as parameters, which could be assumed to be independent of the sample storage conditions and still allow an adequate fit between experimental and predicted values.
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    RESPIRATORY BEHAVIOR OF CHERIMOYA (ANNONA-CHERIMOLA MILL) UNDER CONTROLLED ATMOSPHERES
    (1993) PALMA, T; STANLEY, DW; AGUILERA, JM; ZOFFOLI, JP
    The objective of this work was to obtain information for designing modified-atmosphere packages for storing and transporting cherimoyas. Respiration rates of 'Concha Lisa' cherimoyas at 10C were monitored in a flow-through system using O2 consumption and CO2 production under atmospheres containing 5%, 10%, 15%, or 20% O2. Under normal atmosphere (20% O2), the respiration curve exhibited a typical climacteric rise 15 days after harvest, while 15% and 10% O2 delayed this event. Fruit kept in 5% O2 did not show a detectable climacteric rise and did not produce ethylene. All fruit ripened normally after being transferred to air storage at 20C; however, the time needed to reach an edible condition differed with treatment and was inversely proportional to O2 content. Delay of the climacteric by 5% O2, coupled with the continued ability to ripen, makes this procedure suitable for controlled- or modified-atmosphere cherimoya packaging.